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        <h1 id="1-面向对象和原型链"><a href="#1-面向对象和原型链" class="headerlink" title="1. 面向对象和原型链"></a>1. 面向对象和原型链</h1><h2 id="1-1-面向对象编程"><a href="#1-1-面向对象编程" class="headerlink" title="1.1. 面向对象编程"></a>1.1. 面向对象编程</h2><p>面向对象编程 —— Object Oriented Programming，简称 OOP ，是一种编程开发思想。<br>在面向对象程序开发思想中，每一个对象都是功能中心，具有明确分工，可以完成接受信息、处理数据、发出信息等任务。<br>因此，面向对象编程具有灵活、代码可复用、高度模块化等特点，容易维护和开发，比起由一系列函数或指令组成的传统的过程式编程（procedural programming），更适合多人合作的大型软件项目</p>
<h3 id="1-1-1-面向对象三大特性"><a href="#1-1-1-面向对象三大特性" class="headerlink" title="1.1.1. 面向对象三大特性"></a>1.1.1. 面向对象三大特性</h3><h4 id="1-1-1-1-封装性"><a href="#1-1-1-1-封装性" class="headerlink" title="1.1.1.1. 封装性"></a>1.1.1.1. 封装性</h4><p>将功能的具体实现，全部封装到对象的内部，外界使用对象时，只需要关注对象提供的方法如何使用，而不需要关心对象的内部具体实现，这就是封装。</p>
<h4 id="1-1-1-2-继承性"><a href="#1-1-1-2-继承性" class="headerlink" title="1.1.1.2. 继承性"></a>1.1.1.2. 继承性</h4><p>在 js 中，继承的概念很简单，一个对象没有的一些属性和方法，另外一个对象有，拿过来用，就实现了继承。<br>注意：在其他语言里面，继承是类与类之间的关系，在 js 中，是对象与对象之间的关系。</p>
<h4 id="1-1-1-3-多态性"><a href="#1-1-1-3-多态性" class="headerlink" title="1.1.1.3. 多态性"></a>1.1.1.3. 多态性</h4><p>多态是在强类型的语言中才有的。js 是弱类型语言，所以 JS 不支持多态</p>
<h2 id="1-2-创建对象的方法"><a href="#1-2-创建对象的方法" class="headerlink" title="1.2. 创建对象的方法"></a>1.2. 创建对象的方法</h2><h3 id="1-2-1-字面量创建"><a href="#1-2-1-字面量创建" class="headerlink" title="1.2.1. 字面量创建"></a>1.2.1. 字面量创建</h3><p>字面量创建是由若干名/值对组成的映射表，名/值对中间用冒号分隔，名/值对之间用逗号分隔，整个映射表用花括号括起来。</p>
<p><strong>基本写法</strong>：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> student1 = &#123;</span><br><span class="line">    name : <span class="string">'cocytus'</span>,</span><br><span class="line">    age : <span class="number">23</span>,</span><br><span class="line">    sayName: <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(student1.name);</span><br><span class="line"><span class="built_in">console</span>.log(student1.age);</span><br><span class="line"><span class="built_in">console</span>.log(student1.sayName);</span><br></pre></td></tr></table></figure>
<p><strong>优点</strong>：简单，直观，易懂。</p>
<p><strong>缺点</strong>：① 代码复用性差；② 无法批量生成多个对象，代码冗余度高</p>
<h3 id="1-2-2-内置构造函数"><a href="#1-2-2-内置构造函数" class="headerlink" title="1.2.2. 内置构造函数"></a>1.2.2. 内置构造函数</h3><p><code>ECMAScript</code> 核心语法自带内置构造函数：<code>Function</code>、 <code>Object</code>、 <code>Array</code>、 <code>String</code>、 <code>Number</code>、 <code>Boolean</code>、 <code>RegExp</code>、 <code>Error</code>、 <code>Date</code></p>
<p><strong>基本写法</strong>：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> obj1 = <span class="keyword">new</span> <span class="built_in">Object</span>();</span><br><span class="line">obj1.name = <span class="string">'cocytus'</span>;</span><br><span class="line">obj1.age = <span class="number">23</span>;</span><br><span class="line">obj1.hobby = [<span class="string">'JavaScript'</span>,<span class="string">'HTML'</span>];</span><br><span class="line">obj1.height = <span class="number">175</span>;</span><br><span class="line"><span class="built_in">console</span>.log(obj1);</span><br></pre></td></tr></table></figure>
<p><strong>弊端</strong>：① 创建的对象无法复用；② 代码冗余度高</p>
<h3 id="1-2-3-工厂模式"><a href="#1-2-3-工厂模式" class="headerlink" title="1.2.3. 工厂模式"></a>1.2.3. 工厂模式</h3><p>工厂模式抽象了创建具体对象的过程。因为 ECMAScript 中无法创建类，开发人员就发明了一种函数，用函数来封装以待定接口创建对象的细节。</p>
<p><strong>基本写法</strong>：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line">  <span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 功能：批量创建同一个类型的对象</span></span><br><span class="line"><span class="comment"> * 参数：对象的不同属性值</span></span><br><span class="line"><span class="comment"> * 返回值：当前创建出来的对象</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">createPerson</span>(<span class="params">age,gender,name</span>) </span>&#123;</span><br><span class="line">  <span class="keyword">var</span> person = <span class="keyword">new</span> <span class="built_in">Object</span>();</span><br><span class="line">  person.age = age;</span><br><span class="line">  person.gender = gender;</span><br><span class="line">  person.name = name;</span><br><span class="line">  person.sayName = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">  &#125;;</span><br><span class="line"></span><br><span class="line">  <span class="keyword">return</span> person;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> person1 = create&#123;Person&#125;(<span class="number">18</span>,<span class="string">"male"</span>,<span class="string">"zs"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person1);</span><br><span class="line"><span class="keyword">var</span> person2 = createPerson(<span class="number">20</span>,<span class="string">"male"</span>,<span class="string">"ls"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person2);</span><br><span class="line"><span class="keyword">var</span> person3 = createPerson(<span class="number">19</span>,<span class="string">"male"</span>,<span class="string">"ww"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person3);</span><br></pre></td></tr></table></figure>
<p><strong>优点</strong>：可以批量创建同一种类型的对象</p>
<p><strong>缺点</strong>：没有解决对象识别的问题（看不到对象类型），创建出来的对象都是 Object 类型的。</p>
<h3 id="1-2-4-自定义构造函数模式"><a href="#1-2-4-自定义构造函数模式" class="headerlink" title="1.2.4. 自定义构造函数模式"></a>1.2.4. 自定义构造函数模式</h3><p>为了解决从原型对象生成实例的问题， JavaScript 提供了一个构造函数模式。</p>
<p>所谓“构造函数”，其实就是一个普通函数，但是内部使用了 this 变量，对构造函数使用 new 运算符，就能生成实例，并且 this 变量会绑定在实例对象上。</p>
<p>用构造函数模式将前面的例子重写：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params">age,gender,name</span>)</span>&#123;<span class="comment">//首字母大写</span></span><br><span class="line">    <span class="keyword">this</span>.age = age;</span><br><span class="line">    <span class="keyword">this</span>.gender = gender;</span><br><span class="line">    <span class="keyword">this</span>.name = name;</span><br><span class="line">    <span class="keyword">this</span>.sayName = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        alert(<span class="keyword">this</span>.name);</span><br><span class="line">    &#125;;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> person1 = <span class="keyword">new</span> Person(<span class="number">18</span>,<span class="string">"male"</span>,<span class="string">"zs"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person1);</span><br><span class="line"><span class="keyword">var</span> person2 = <span class="keyword">new</span> Person(<span class="number">20</span>,<span class="string">"male"</span>,<span class="string">"ls"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person2);</span><br><span class="line"><span class="keyword">var</span> person3 = <span class="keyword">new</span> Person(<span class="number">19</span>,<span class="string">"male"</span>,<span class="string">"ww"</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person3);</span><br></pre></td></tr></table></figure>
<p><strong>注意</strong>：必须使用 new 操作符，这种方式调用构造函数实际上经历了以下 4 个步骤：</p>
<ol>
<li>创建了一个新的空对象</li>
<li>将构造函数的作用域赋给新对象（因此 this 就指向了这个新对象）</li>
<li>执行了这个构造函数的函数体</li>
<li>返回新对象</li>
</ol>
<p><strong>优点</strong>：可以批量创建，只要需要每一次 new 一个即可，并且可以看到具象化的类型</p>
<h3 id="1-2-5-构造函数的存在的问题"><a href="#1-2-5-构造函数的存在的问题" class="headerlink" title="1.2.5. 构造函数的存在的问题"></a>1.2.5. 构造函数的存在的问题</h3><p>使用构造函数带来的最大的好处就是创建对象更方便了，但是其本身也存在一个浪费内存的问题：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params">name, age</span>)</span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name;</span><br><span class="line">    <span class="keyword">this</span>.age = age;</span><br><span class="line">    <span class="keyword">this</span>.sayHi = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">"你今天吃了吗"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> person1 = <span class="keyword">new</span> Person(<span class="string">"zs"</span>, <span class="number">20</span>);</span><br><span class="line"><span class="built_in">console</span>.log(p);</span><br><span class="line">person1.sayHi();</span><br><span class="line"><span class="keyword">var</span> person2 = <span class="keyword">new</span> Person(<span class="string">"ls"</span>, <span class="number">16</span>);</span><br><span class="line"><span class="built_in">console</span>.log(p2);</span><br><span class="line">person2.sayHi();</span><br><span class="line"><span class="comment">// 因为是两个新对象，内存地址不相同</span></span><br><span class="line"><span class="built_in">console</span>.log(person1 == person2); <span class="comment">// false</span></span><br><span class="line"><span class="built_in">console</span>.log(person1.sayHi == person2.sayHi); <span class="comment">//  false</span></span><br></pre></td></tr></table></figure>
<p>因为每个对象上都有属于自己的 sayHi 方法，然而两个 sayHi 方法并不是同一个 Function 实例。不同实例上的同名函数是不相等的。<br>假如创建了 100 个对象，那么在内存里面就会创建 100 个 sayHi 函数，这样会造成内存浪费的问题。其实在内存里面只需要一份 sayHi 方法就行了。<br>　　所以我们把函数定义转移到构造函数之外来解决这个问题。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params">name, age</span>)</span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name;</span><br><span class="line">    <span class="keyword">this</span>.age = age;</span><br><span class="line">    <span class="keyword">this</span>.sayHi = sayHi();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">sayHi</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">"你今天吃了吗"</span>)；</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> person1 = <span class="keyword">new</span> Person(<span class="string">"zs"</span>, <span class="number">20</span>);</span><br><span class="line"><span class="keyword">var</span> person2 = <span class="keyword">new</span> Person(<span class="string">"ls"</span>, <span class="number">16</span>);</span><br><span class="line"><span class="built_in">console</span>.log(person1.sayHi == person2.sayHi); <span class="comment">// true</span></span><br></pre></td></tr></table></figure>
<p>我们把 sayHi()函数的定义转移到了构造函数外部，而在构造函数内部，我们将 sayHi 属性设置成等于全局的 sayHi 函数。这样由于 sayHi 包含的是一个指向函数的指针，因此 person1 和 person2 对象就共享在全局作用域中定义的同一个 sayHi()函数。</p>
<p>但是这样全局作用域中定义的函数实际上只能被某个对象调用，而且如果对象需要定义很多方法，那么就要定义很多个全局函数。就会暴漏很多的函数，容易造成全局变量污染。</p>
<h3 id="1-2-6-原型模式"><a href="#1-2-6-原型模式" class="headerlink" title="1.2.6. 原型模式"></a>1.2.6. 原型模式</h3><p><code>Javascript</code> 规定，每一个构造函数都有一个 <code>prototype</code> 属性，指向另一个对象。这个对象的所有属性和方法，都会被构造函数的实例继承。这也就意味着，我们可以把所有对象实例需要共享的属性和方法直接定义在 <code>prototype</code> 对象上。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 构造函数</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// console.dir(Person);</span></span><br><span class="line"><span class="comment">// console.log(Person.prototype);</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 原型对象</span></span><br><span class="line"><span class="comment">// 这是给原型对象添加color属性</span></span><br><span class="line">Person.prototype.color = <span class="string">"lime"</span>;</span><br><span class="line">Person.prototype.gender = <span class="string">"male"</span>;</span><br><span class="line"><span class="comment">// 把sayHi方法添加给原型，谁可以访问</span></span><br><span class="line"><span class="comment">// 构造函数创建的实例就可以访问到了</span></span><br><span class="line">Person.prototype.sayHi = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">"hello"</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">// console.log(Person.prototype);</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 实例对象：person1</span></span><br><span class="line"><span class="keyword">var</span> person1 = <span class="keyword">new</span> Person();</span><br><span class="line"><span class="comment">// console.log(p.color); // lime</span></span><br><span class="line"><span class="comment">// console.log(p.gender); // male</span></span><br><span class="line"><span class="comment">// p.sayHi();</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 实例对象：person2</span></span><br><span class="line"><span class="keyword">var</span> person2 = <span class="keyword">new</span> Person();</span><br><span class="line"><span class="built_in">console</span>.log(person2); <span class="comment">// 是个空对象</span></span><br><span class="line">p2.sayHi();</span><br><span class="line"></span><br><span class="line"><span class="comment">// person1的sayHi和person2的sayHi是同一个函数</span></span><br><span class="line"><span class="comment">// 来源于原型上的sayHi方法</span></span><br><span class="line"><span class="comment">// 这样就解决了内存浪费问题</span></span><br><span class="line"><span class="built_in">console</span>.log(p.sayHi == p2.sayHi); <span class="comment">// true</span></span><br></pre></td></tr></table></figure>
<h2 id="1-3-原型、构造函数、实例、原型链"><a href="#1-3-原型、构造函数、实例、原型链" class="headerlink" title="1.3. 原型、构造函数、实例、原型链"></a>1.3. 原型、构造函数、实例、原型链</h2><p><img src="https://camo.githubusercontent.com/803a654869fa6a06847ee34b4ef91aed4daee13e/687474703a2f2f696d672e736d79687661652e636f6d2f32303138303330365f313534302e706e67" alt="关系图"></p>
<p><strong>构造函数</strong>：构造函数就是一个函数，配合 new 可以新建对象。构造函数中有一个 <code>prototype</code> 属性，这个属性是一个指针，指向它的原型对象。</p>
<p><strong>实例</strong>：通过<strong>构造函数</strong>创建出来的对象我们把它叫做构造函数的实例。一个构造函数可以有很多实例。实例一创造出来就具有 <code>constructor</code> 属性（指向构造函数）和<code>__proto__</code>属性（指向原型对象）。</p>
<p><strong>原型</strong>：每一个构造函数都有一个属性<code>prototype</code>，函数的 <code>prototype</code> 属性值就是原型。通过构造函数创建出来的实例能够直接使用原型上的属性和方法。</p>
<h3 id="1-3-1-proto-属性"><a href="#1-3-1-proto-属性" class="headerlink" title="1.3.1. __proto__属性"></a>1.3.1. <code>__proto__</code>属性</h3><p>任意一个对象，都会有<code>__proto__</code>属性，这个属性指向了构造函数的 <code>prototype</code> 属性，也就是原型对象。</p>
<p>获取原型对象：</p>
<ul>
<li>通过 <code>构造函数.prototype</code> 可以获取</li>
<li>通过 <code>实例.__proto__</code> 可以获取（隐式原型）</li>
<li>它们指向了同一个对象 <code>构造函数.prototype === 实例.__proto__</code></li>
</ul>
<p><strong>注意</strong>：<code>__proto__</code> 是浏览器的一个隐藏（私有）属性，早期的 IE 浏览器不支持，所以说不要在线上项目中去使用它。本地开发中可以通过实例知道实例对象可以访问原型上的哪些成员。不要通过它来修改原型里的内容，如果要修改原型中的内容，使用 <code>构造函数.prototype</code> 去修改.</p>
<h3 id="1-3-2-constructor-属性"><a href="#1-3-2-constructor-属性" class="headerlink" title="1.3.2. constructor 属性"></a>1.3.2. constructor 属性</h3><p>默认情况下，原型对象中只包含了一个属性：constructor，constructor 属性指向了当前的构造函数。</p>
<h2 id="1-4-原型链"><a href="#1-4-原型链" class="headerlink" title="1.4. 原型链"></a>1.4. 原型链</h2><h3 id="1-4-1-原型链概念"><a href="#1-4-1-原型链概念" class="headerlink" title="1.4.1. 原型链概念"></a>1.4.1. 原型链概念</h3><p>任何一个对象，都有原型对象，原型对象本身又是一个对象，所以原型对象也有自己的原型对象，这样一环扣一环就形成了一个链式结构，我们把这个链式结构称为：<strong>原型链</strong>。</p>
<p>绘制对象的原型链结构：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//1. var p = new Person();</span></span><br><span class="line"><span class="comment">//2. var o = new Object();</span></span><br><span class="line"><span class="comment">//3. var arr = new Array();</span></span><br><span class="line"><span class="comment">//4. var date = new Date();</span></span><br><span class="line"><span class="comment">//5. Math</span></span><br><span class="line"><span class="comment">//6. 查看一个div的原型链结构</span></span><br></pre></td></tr></table></figure>
<p>总结：在访问一个实例的时候，如果实例本身没找到此方法或属性，就往原型上找。如果还是找不到，继续往上一级的原型上找。Object.prototype 是原型链的尽头，Object.prototype 的原型是 null。</p>
<h3 id="1-4-2-属性查找原则"><a href="#1-4-2-属性查找原则" class="headerlink" title="1.4.2. 属性查找原则"></a>1.4.2. 属性查找原则</h3><p>如果是获取操作</p>
<ol>
<li>会先在自身上查找，如果没有</li>
<li>则根据<code>__proto__</code>对应的原型去找，如果没有</li>
<li>一直找到<code>Object.prototype</code>，如果没有，那就找不到了。</li>
</ol>
<p>如果是修改操作：</p>
<p>只会修改对象自身的属性，如果自身没有这个属性，那么就会添加这个属性，并不会修改原型中的属性。</p>
<h3 id="1-4-3-Object-prototype-对象的方法"><a href="#1-4-3-Object-prototype-对象的方法" class="headerlink" title="1.4.3. Object.prototype 对象的方法"></a>1.4.3. Object.prototype 对象的方法</h3><h4 id="1-4-3-1-hasOwnProperty"><a href="#1-4-3-1-hasOwnProperty" class="headerlink" title="1.4.3.1. hasOwnProperty()"></a>1.4.3.1. <code>hasOwnProperty()</code></h4><p><strong>语法</strong>：对象.hasOwnProperty(“属性”);</p>
<p><strong>作用</strong>：该方法会返回一个布尔值，判断对象是否具有指定的属性是自身的属性。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  name: <span class="string">"zs"</span></span><br><span class="line">&#125;;</span><br><span class="line"><span class="comment">//判断name属性是不是obj自己提供的</span></span><br><span class="line"><span class="built_in">console</span>.log(obj.hasOwnProperty(<span class="string">"name"</span>)); <span class="comment">//true</span></span><br><span class="line"><span class="built_in">console</span>.log(obj.hasOwnProperty(<span class="string">"toString"</span>)); <span class="comment">//false</span></span><br></pre></td></tr></table></figure>
<p>in 运算符：<br><strong>语法</strong>： “属性” in 对象<br><strong>作用</strong>： 判断该属性能否被对象访问到，也就是说，不管这个属性是对象自身的，还是来源于原型链上，只要能够访问到，就返回 true</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params">name</span>)</span>&#123;</span><br><span class="line"><span class="keyword">this</span>.name = name;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> p = <span class="keyword">new</span> Person(<span class="string">"zs"</span>);</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"name"</span> <span class="keyword">in</span> p); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"hasOwnProperty"</span> <span class="keyword">in</span> p); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"toString"</span> <span class="keyword">in</span> p); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"push"</span> <span class="keyword">in</span> []); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(p.hasOwnProperty(<span class="string">"hasOwnProperty"</span>)); <span class="comment">// false</span></span><br></pre></td></tr></table></figure>
<p><code>hasOwnProperty()</code> 与 in 的区别<br>in 操作符：如果属性不是自己提供的，是从原型上继承来的，也会返回 true</p>
<p><code>hasOwnProperty():</code> 该属性必须是自己提供，才返回 true，否则返回 false。</p>
<h4 id="1-4-3-2-isPrototypeOf"><a href="#1-4-3-2-isPrototypeOf" class="headerlink" title="1.4.3.2. isPrototypeOf()"></a>1.4.3.2. <code>isPrototypeOf()</code></h4><p><strong>语法</strong>：对象 A.isPrototypeOf(对象 B);<br><strong>作用</strong>：该方法用于测试一个对象是否存在于另一个对象的原型链上。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//判断A对象是否在B对象的原型链上。</span></span><br><span class="line"><span class="comment">//返回值：true，在原型链上    false：不在原型链上。</span></span><br><span class="line">A.isPrototetypeOf(B);</span><br></pre></td></tr></table></figure>
<h4 id="1-4-3-3-propertyIsEnumerable"><a href="#1-4-3-3-propertyIsEnumerable" class="headerlink" title="1.4.3.3. propertyIsEnumerable()"></a>1.4.3.3. <code>propertyIsEnumerable()</code></h4><p>该方法返回一个布尔值，表明指定的属性名是否是当前对象可枚举的自身属性。</p>
<p>该方法可以判断出指定对象里的属性是否可枚举，也就是说该属性是否可以通过 for…in 循环等遍历到，不过有些属性虽然可以通过 for…in 循环遍历到，但因为它们不是自身属性，而是从原型链上继承的属性,所以该方法也会返回 false。如果对象没有指定的属性，该方法返回 false。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//1. 判断这个属性能不能被遍历(必须是自己的属性）。</span></span><br><span class="line">obj.propertyIsEnumerable(prop);</span><br></pre></td></tr></table></figure>
<h4 id="1-4-3-4-toLocaleString-toString"><a href="#1-4-3-4-toLocaleString-toString" class="headerlink" title="1.4.3.4. toLocaleString()/toString()"></a>1.4.3.4. toLocaleString()/toString()</h4><p><code>toString()</code> 方法返回一个表示该对象的字符串。格式：[object Object],内置对象都重写了 toString 方法。</p>
<p><code>toLocaleString()</code> 方法返回一个该对象的字符串表示。该方法主要用于被本地化相关对象覆盖。</p>
<h4 id="1-4-3-5-valueOf"><a href="#1-4-3-5-valueOf" class="headerlink" title="1.4.3.5. valueOf()"></a>1.4.3.5. <code>valueOf()</code></h4><p><code>valueOf()</code> 方法返回指定对象的原始值。</p>
<p><strong>语法</strong>：</p>
<p><strong>作用</strong>：<br>　　<code>valueOf()</code>把对象转换成原始类型的值（数值、字符串和布尔值），很少需要显式的调用此函数；当遇到需要转换成一个原始值的情况时， JavaScript 会自动调用此方法。默认情况下, <code>valueOf()</code> 会被每个对象 Object 继承。每一个内置对象都会覆盖这个方法为了返回一个合理的值，如果对象没有原始值，<code>valueOf()</code> 就会返回对象自身。</p>
<h3 id="1-4-4-instanceof"><a href="#1-4-4-instanceof" class="headerlink" title="1.4.4. instanceof()"></a>1.4.4. <code>instanceof()</code></h3><p><img src="https://camo.githubusercontent.com/9996f26d7a4e9df5ab87a962689d42de99943855/687474703a2f2f696d672e736d79687661652e636f6d2f32303138303330365f323230392e706e67" alt="instanceof"></p>
<p><code>instanceof</code> 运算符用来测试一个对象的原型链中是否存在一个构造函数的 <code>prototype</code> 属性。作用和 <code>isPrototypeOf</code> 类似</p>
<p><strong>语法</strong>： 实例对象 <code>instanceof</code> 构造函数</p>
<p><strong>作用</strong>：检测构造函数的 <code>prototype</code> 属性是否在实例对象的原型链上。</p>
<ul>
<li>A.isPrototypeOf(B) 判断 A 是否在 B 的原型链上 A： 是一个原型对象</li>
<li>B instanceof A 判断 A 的 prototype 是否在 B 的原型链上 A：是一个构造函数</li>
</ul>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#1-面向对象和原型链"><span class="nav-text">1. 面向对象和原型链</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#1-1-面向对象编程"><span class="nav-text">1.1. 面向对象编程</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-1-1-面向对象三大特性"><span class="nav-text">1.1.1. 面向对象三大特性</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#1-1-1-1-封装性"><span class="nav-text">1.1.1.1. 封装性</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-1-1-2-继承性"><span class="nav-text">1.1.1.2. 继承性</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-1-1-3-多态性"><span class="nav-text">1.1.1.3. 多态性</span></a></li></ol></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#1-2-创建对象的方法"><span class="nav-text">1.2. 创建对象的方法</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-1-字面量创建"><span class="nav-text">1.2.1. 字面量创建</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-2-内置构造函数"><span class="nav-text">1.2.2. 内置构造函数</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-3-工厂模式"><span class="nav-text">1.2.3. 工厂模式</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-4-自定义构造函数模式"><span class="nav-text">1.2.4. 自定义构造函数模式</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-5-构造函数的存在的问题"><span class="nav-text">1.2.5. 构造函数的存在的问题</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2-6-原型模式"><span class="nav-text">1.2.6. 原型模式</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#1-3-原型、构造函数、实例、原型链"><span class="nav-text">1.3. 原型、构造函数、实例、原型链</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-3-1-proto-属性"><span class="nav-text">1.3.1. __proto__属性</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-3-2-constructor-属性"><span class="nav-text">1.3.2. constructor 属性</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#1-4-原型链"><span class="nav-text">1.4. 原型链</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-4-1-原型链概念"><span class="nav-text">1.4.1. 原型链概念</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-4-2-属性查找原则"><span class="nav-text">1.4.2. 属性查找原则</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-4-3-Object-prototype-对象的方法"><span class="nav-text">1.4.3. Object.prototype 对象的方法</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#1-4-3-1-hasOwnProperty"><span class="nav-text">1.4.3.1. hasOwnProperty()</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-4-3-2-isPrototypeOf"><span class="nav-text">1.4.3.2. isPrototypeOf()</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-4-3-3-propertyIsEnumerable"><span class="nav-text">1.4.3.3. propertyIsEnumerable()</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-4-3-4-toLocaleString-toString"><span class="nav-text">1.4.3.4. toLocaleString()/toString()</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#1-4-3-5-valueOf"><span class="nav-text">1.4.3.5. valueOf()</span></a></li></ol></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-4-4-instanceof"><span class="nav-text">1.4.4. instanceof()</span></a></li></ol></li></ol></li></ol></div>
            

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    var isfetched = false;
    var isXml = true;
    // Search DB path;
    var search_path = "search.xml";
    if (search_path.length === 0) {
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    } else if (/json$/i.test(search_path)) {
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    // monitor main search box;

    var onPopupClose = function (e) {
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      $('#local-search-input').val('');
      $('.search-result-list').remove();
      $('#no-result').remove();
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    function proceedsearch() {
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      $localSearchInput.attr("autocorrect", "off");
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      // start loading animation
      $("body")
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          '<div id="search-loading-icon">' +
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          '</div>' +
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          var resultContent = document.getElementById(content_id);
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                var searchTextCount = 0;
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                        position = item.position;
                        word = item.word;
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                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
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                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
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                    var end = position + 80;
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                  // sort slices in content by search text's count and hits' count

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                  // select top N slices in content

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                  // highlight title and content

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                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
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                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
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                } else if (resultLeft.hitCount !== resultRight.hitCount) {
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                } else {
                  return resultRight.id - resultLeft.id;
                }
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              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
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              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
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          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
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